After I installed 4.1.10, I've been unable to run any of my virtual machines. Downgrading to 4.1.8 does not appear to have helped. The guest is Debian, the host OS X 10.7.3. Attached is the VBox.log and VBox.png from one of the crashes.

After starting the VM, I see the GRUB boot screen and am able to select a boot option. It seems to crash while trying to load initrd.

Trying to repair disk permissions will do nothing for this problem. Something else has taken over virtualization. The other application has to be stopped, and if that doesn't help and something else went wrong, the system may need to be rebooted.

Unrelated, but just in case I missed something: Is the screenshot of a blank screen meant to convey some meaningful information or was it attached just to waste a bit of bandwidth?

At any rate, it's very unusual for VT-x to be unavailable on Apple hardware. So the fact that it's unavailable does likely signify a problem. Maybe as simple as another virtualizer running, maybe something deeper.

Disk Utility reported some ruby programs having incorrect permissions. Fixing them did not fix VirtualBox.

The blank screen was attached because the error message suggested sending the log and the screenshot. I had expected it to display the "Loading initrd..." message, actually, but didn't check it before uploading.

I did install something to aid the new Android emulator, but am not currently running the emulator. I even tried unloading that kext, and VirtualBox still fails.

I also have Parallels Desktop 6 installed to run my Boot Camp partition. I've had this installed for some time. Unloading its hypervisor kext doesn't allow Virtualbox to run. Parallels can start a Linux VM fine.

Is there anything in particular I should be looking for? Also, thanks for the assistance.

I guess we'll need to update our instructions to say to upload a screenshot only if it contains any actual information

My suggestion, try rebooting the host (possibly powering off and on to be really sure). See if that will allow VirtualBox to allow hardware virtualization. Your CPU can do it, and it should be available.

As a side note, if downgrading to the previously working version didn't help, there must be something else causing trouble. Maybe upgrading VirtualBox had nothing to do with it.

Oh, VirtualBox runs without VT-x too. But not everything works, and apparently your guest is one of those that don't. 32-bit Windows guests usually aren't a problem, Linux is a toss-up because the configuration can be just about anything.